Rebar Coupler With Fine-Thread Preload to Prevent Slippage
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Solution Overview
Problem
Existing couplers for threaded reinforcing bars in concrete construction suffer from slippage due to loose tolerances and inability to rotate, which complicates installation and does not meet construction standards.
Innovation Solution
A coupler design featuring a first fitting with a coarse external thread and a finer internal thread, along with a frangible plug that applies a preload to the reinforcing bar, allowing for secure engagement even in situations where rotation is restricted.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a coarse pitch thread is used for mounting fittings on reinforcing bars, then the fitting can be easily manufactured and installed, but slippage occurs between the fitting and bar under high loads
Solution Approach 1:
The fitting is divided into two distinct threading sections: a first internal thread with coarse pitch for mounting the fitting on the reinforcing bar, and a second internal thread with fine pitch for engaging the plug. This segmentation allows each thread to be optimized for its specific function - the coarse thread for easy installation and the fine thread for preventing slippage under load.
Solution Approach 2:
Different parts of the fitting have different thread pitches tailored to their specific requirements. The first internal thread portion has a coarse pitch matching the reinforcing bar for easy installation, while the second internal thread portion has a fine pitch for high-load engagement with the plug, creating local quality variations within a single component.
2Reliability
If epoxy cement is used to fill the coupler interior, then slippage is prevented, but installation time and cost increase
Solution Approach 1:
The invention replaces the chemical bonding mechanism of epoxy cement with a mechanical preload system. The plug, when tightened in the fine pitch second internal thread, applies a mechanical preload force against the reinforcing bar end, creating friction that prevents slippage without requiring chemical adhesives or additional installation steps.
3Adaptability or versatility
If rotation of reinforcing bars is restricted during installation, then coupling cannot be achieved with conventional methods, but the invention enables coupling under these conditions
Solution Approach 1:
The reinforcing bar is first inserted into the fitting without requiring rotation, and only after the bar is in position does the operator rotate the plug within the fine pitch second internal thread to apply the preload. This preliminary positioning followed by selective rotation enables installation where bar rotation is restricted.
Solution Approach 2:
The system transitions from a static insertion phase to a dynamic preload application phase. During insertion, no rotation is needed; once positioned, the plug is rotated to generate the preload force. This dynamic approach allows the system to adapt to restricted rotation conditions while still achieving the required mechanical engagement.
4Reliability
If a finer pitch thread is used for the plug, then preload is applied effectively, but the thread engagement complexity increases
Solution Approach 1:
The fitting's internal thread is segmented into two distinct sections with different pitches. The first section uses a coarse pitch for easy bar insertion, while the second section uses a fine pitch for precise plug engagement and preload application. This segmentation manages complexity by assigning specific functions to specific thread sections.
Solution Approach 2:
The fitting serves multiple functions through its dual-thread design: it mounts the reinforcing bar via the coarse first internal thread and simultaneously engages the plug via the fine second internal thread to apply preload. This multi-functionality consolidates what could be separate components into a single integrated fitting.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The coupler effectively minimizes slippage and ensures secure connections by utilizing a finer pitch thread for preload, reducing installation torque, and accommodating loose tolerances, thus meeting construction standards.
Implementation Method 1
The plug is adapted for being tightened in said second internal thread for applying a preload against said end of said threaded reinforcing bar
Implementation Method 2
a first internal thread for threadedly inserting the first externally threaded reinforcing bar into the first fitting
Data Source
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AI summary
A coupler including: a first fitting for mounting to a first externally threaded reinforcing bar for use in concrete construction, the first fitting comprising a first body having a first internal thread for threadedly inserting the first externally threaded reinforcing bar into the first fitting; the first fitting having a second internal thread having a pitch finer than a pitch of the first internal thread; and a plug for threading into the second internal thread for abutting an end of said threaded reinforcing bar.